A reciprocating electric compressor (hereinafter simply referred to as “compressor”) employed in refrigerating-cycle devices such as a refrigerator with a freezer, a vending machine, and an air-conditioner has been required to be highly efficient and reliable. In general, a conventional compressor is equipped with a crankshaft incorporating a lubricator, and a typical one is disclosed in Japanese Patent Publication No. S62-44108. The conventional compressor is described hereinafter with reference to FIG. 8.
FIG. 8 is a sectional view of the conventional compressor. Compressor 1 is housed in enclosed container 2, which accommodates frame 3 in the middle, motor unit 4 at a lower section, compressing mechanism 5 at an upper section. Crankshaft 7 extends through bearing 6 of frame 3. On an outer wall of crankshaft 7, rotor 8 of motor unit 4 is rigidly mounted. Crankshaft 7 has main shaft 70 and eccentric shaft 9, and engages with slider 11 of piston 10 via eccentric shat 9. Piston 10 is an element of compressing mechanism 5.
Slant hole 12 (hereinafter referred to simply as “hole”) slantingly extends from the bottom of crankshaft 7 to the lower end of bearing 6 through crankshaft 7, and opens onto the outer wall of shaft 7. Hole 12 has a rather small diameter.
A part of crankshaft 7 rests within bearing 6, and on this resting section, spiral pump 14 (hereinafter referred to simply as “pump”) is formed. Pump 14 comprises a single leading groove which communicates with lateral hole 13 at its lower end and vertical hole 15 formed in eccentric shaft 9 at its upper end. Vertical hole 15 opens into an inner space of container 2 at its upper end, and communicates with the slide face of thrust-bearing 16 at its lower end. Lubricant oil 17 is pooled in the lower section of container 2, and crankshaft 7 dips therein at its lower end.
An operation of the foregoing conventional reciprocating compressor is described hereinafter. When motor unit 4 is turned on, rotor 8 starts spinning, which causes crankshaft 7 to rotate. Rotation of crankshaft 7 reciprocates piston 10 engaging with eccentric shaft 9 via slider 11, so that compression is carried out. Lubricant oil 17 rises from the lower end of crankshaft 7 through slanted hole 12 due to centrifugal force, and moves upward via lateral hole 13 to pump 14 of main shaft 70, which then transmits lubricant oil 17 to bearing 16 and eccentric shaft 9, and then lubricant oil 17 is discharged into the space within container 2.
As such, lubricant oil 17 rises through hole 12, which extends slantingly and upward from the lower end of shaft 7, due to centrifugal force, and pump 14 formed of the one-way leading groove from lateral hole 13 transfers lubricant oil 17 to the slide section of bearing 16, where lubricant oil 17 performs lubricating action. A winding direction of the leading groove is determined on the premise that pump 14 operates in a given rotating direction. Therefore, if pump 14 operates in a direction opposite to the given one, a downward force is created by pump 14, so that no lubricant oil is supplied to the upper section of bearing 6. As a result, bearing 6 incurs abnormal abrasion, which causes a breakdown. For instance, in the case of a reciprocating compressor which employs a three-phase induction motor as the motor unit, it can be inversely rotated due to incorrect wiring. Thus a plugging relay needs to be integrated into the circuit for preventing the breakdown due to the reverse rotation; however, since the relay is so expensive, the cost of the compressor is obliged to increase.
There is another conventional reciprocating compressor which employs a single-phase and resistant-start induction motor using a PTC relay as a starter. In this compressor, when an instantaneous power interruption occurs, which does not give a recovery time to the PTC relay, the piston is pushed back due to the pressure of a compressed room. If the power is recovered during this reverse rotation, the compressor is kept rotating inversely. In this case, the lubricator does not work properly, and the slide section incurs a breakdown due to abrasion.
In order to overcome the problems discussed above, a reciprocating compressor equipped with both-way leading grooves has been proposed. This structure allows reversible operation; however, there is still no reciprocating compressor operable in both rotating directions and equipped with a compressing unit, which needs high pump-head for lubrication, over a motor unit.